1. Field of the Invention
This invention relates to an ink ejecting printing apparatus formed using a piezoelectric ceramic. In particular, this invention relates to an ink ejecting printing apparatus which prints characters in different grades of resolution or modes by controlling the application of a voltage to the piezoelectric ceramic.
2. Description of the Related Art
Among non-impact-type printing heads which are conventional impact-type printing heads, ink-ejecting-type printing heads generally have the simplest operating principles and are best suited for multi-level printing and color printing. In particular, among the ink-ejecting-type printing heads, a drop-on-demand-type printing head which ejects ink drops only on demand is prevailing in the market because of its good ejecting efficiency and low running cost.
Typical drop-on-demand-type non-impact printing systems include a Kyser-type printing system, as disclosed in U.S. Pat. No. 3,946,398, and a thermal-ejecting-type printing system, as disclosed in U.S. Pat. No. 4,723,129. However, these systems have a number of difficult problems. The Kyser-type printhead has a problem in that it is difficult to miniaturize. The thermal-ejecting-type printing head has a problem in that a heat-tolerant ink is required, since a high temperature is applied to the ink. Therefore, as a new system to solve both of the above-mentioned problems simultaneously, an ink ejecting printing apparatus using a shearing-mode-type printing head, as disclosed in U.S. Pat. No. 4,879,568, has been proposed.
In the shearing-mode-type ink ejecting printing apparatuses, in general, a number of printing modes can be set, including: a normal printing mode; an ink saving printing mode; a high-speed printing mode, and a high-quality printing mode. In the normal printing mode, printing is performed by ejecting ink drops out of a nozzle in a 1:1 ratio to the respective dot printing signals of the printing data. In the ink saving printing mode, printing is performed by deleting a predetermined number of dots from the total number of dots to be printed based on the respective dot printing signals. In the high-speed printing mode, printing is performed by ejecting ink drops by deleting a predetermined number of dots from the total number of dots to be printed based on the respective dot printing signals and by moving the printing head relative to a printing paper at a faster scanning speed than the scanning speed used in the normal printing mode. In the high-quality printing mode; printing is performed at twice the resolution used in the normal printing mode.
However, there is a problem associated with the ink saving printing mode and the high speed printing mode in a conventional ink ejecting printing apparatus. In the conventional ink ejecting printing apparatus, as shown in FIG. 18, the pitch between dots in the main scanning direction and the pitch between dots in sub-scanning direction are the same. Accordingly, when an ink saving mode is set, if the predetermined number of ink dots are deleted simply by deleting every other dot, void points are produced, as shown in FIG. 19. In order to print in the ink saving mode without creating void points, a complicated process is needed, which can increase the cost of the ink ejecting printing apparatus.
In an ink ejecting printing apparatus there is also a problem associated with changing between the normal and high-quality modes in which both the normal mode and a high quality mode can be set. When printing in the normal printing mode, as shown in FIG. 20, the pitch between dots in the main scanning direction is the same as the pitch between dots in the sub-scanning direction. When printing in the high quality mode, the pitch between dots in both main scanning and sub-scanning directions is 1/2 the pitch between dots in the normal printing mode, but the proper ink quantity is difficult to control. Therefore, when printing in the high quality mode, as shown in FIG. 21, the dot diameter becomes too large when an ink drop impacts the printing paper. Thus, a desired quality, which is expected in the high quality mode, cannot be obtained. Because of this, when printing in the high quality mode, a special printing paper, on which ink runs less than on a normal printing paper, is used to keep the dot diameter small. However, the special paper is very expensive and the running cost of the ink ejecting printing apparatus increases significantly.